15-Year vs 30-Year Mortgage: The Real Trade-Off

A 15-year mortgage saves substantial interest compared to a 30-year loan — but that's only half the picture. The right choice depends heavily on what you'd otherwise do with the monthly payment difference.

Why 15-year loans save so much interest

Two effects compound together: a shorter loan term means less total time for interest to accrue, and 15-year mortgages typically carry a meaningfully lower interest rate than 30-year loans (often 0.5-0.75 percentage points less), since lenders view the shorter commitment as lower risk. Combined, total interest paid over a 15-year loan is often less than half of what the same loan amount would cost over 30 years.

The monthly payment reality

Despite the interest savings, a 15-year mortgage's monthly payment is substantially higher than a 30-year loan for the same amount — often 40-50% higher — since you're paying off the same principal in half the time. This higher required payment reduces monthly cash flow flexibility and can limit how much home some buyers can qualify for in the first place.

The real question: what would you do with the difference?

If you took the 30-year loan and invested the monthly payment difference in the stock market instead, historical average market returns (~7% real, long-run) often exceed the interest rate you'd save with a 15-year mortgage — meaning the 30-year-plus-invest strategy can mathematically outperform the 15-year loan over the long run, assuming market returns hold and you actually stick to investing the difference consistently.

Why many people still prefer the 15-year anyway

Guaranteed debt payoff versus uncertain market returns is a real trade-off, not just a math problem — a 15-year mortgage guarantees the interest savings, while investing instead depends on actual market performance, which varies and could underperform in any given period. Some people also simply value being debt-free sooner for peace of mind, independent of which option wins on a spreadsheet.

A middle-ground option

Taking a 30-year mortgage but voluntarily making extra principal payments (without being contractually obligated to the higher 15-year payment) offers flexibility — you get the lower guaranteed monthly payment, but can pay it down faster in good months and fall back to the lower required payment if money gets tight in a given month.

Compare your specific numbers

The free Mortgage Comparison Calculator compares 15-year vs 30-year terms side by side directly. The Mortgage Calculator shows your full amortization schedule for either term individually.